Kinetic energy cavity penetrator weapon

ABSTRACT

A method to increase the penetration of kinetic energy penetrating weapons designed to engage hardened and hardened deeply buried targets. The concept utilizes a projecting nose pin on the front of the penetrator to establish a terradynamic cavity similar to hydrodynamic cavities generated when certain projectiles penetrate water at velocities sufficient to penetrate in a supercavitation mode. The creation of a terradynamic cavity in which only the nose pin is in contact with the material being penetrated significantly reduces the drag of the penetrator enabling it to penetrate deeper into various media than other more conventional designs. The invention uses two modes of penetration. A guided mode is employed where the penetrator, with its projecting nose pin, normally would be unstable and is maintained stable in a straight-line trajectory utilizing an inverse, angle-angle rate guidance law and jet reaction control system. The guided mode also can be used on a normally unstable penetrator penetrating in a cavity penetration mode to change the trajectory and guide the penetrator on a predetermined path using best remaining path guidance concepts. An unguided penetrator mode utilizes a standoff pin which reduces the drag but is tailored so that the penetrator, in the penetration process, is normally stable and penetrates in a straight-line.

BACKGROUND OF THE INVENTION

[0001] This invention relates to weapons designed to engage hardened and hardened deeply buried targets. The field of invention also includes weapons designed to engage targets under composite protection such as concrete-soil-concrete laminates and water-soil-concrete laminates.

[0002] The design of hard target weapons has evolved based on testing conducted by Sandia National Laboratories in the time frame 1960-2000. The design parameters identified in these investigations have evolved to an empirical design equation, often referred to as Young's Equation, which states that the penetration depth of a kinetic energy penetrator is directly proportional to the cross-sectional area density, the soil factor through which the target is penetrating, a nose factor, and the velocity at impact. The nose factor in this calculation is taken to be in the range of 0.75 to 0.95 depending on the nose shape. The soil factor is typically five for dirt and one for concrete. Values of “soil” factor have been determined empirically for a wide variety of materials. The threshold velocity is usually taken to be 100 feet-per-second. The form of Young's Equation is usually: $D = {C_{1} - N - S - {\frac{W^{m}}{A}\quad \left( {V - V_{THRESHOLD}} \right)}}$

[0003] where

[0004] D=Depth of Penetration

[0005] C₁=A Constant

[0006] N=Nose Factor

[0007] S=Soil Factor

[0008] W=Weight of the Penetrator

[0009] A=Cross Sectional Area of Penetrator

[0010] V=Impact Velocity

[0011] m=A Constant Between 0.7 and 1.0

[0012] The design objectives to achieve maximum penetration depth focus on selection of the parameters in the empirical equation to provide maximum penetration depth. This is accomplished while maintaining a stabilized, penetrating trajectory which is a trajectory which does not include J. hooking instabilities or diversion of the penetrator off its intended path. A typical design concept for penetrators evolved under prior state of the art is a BLU-109 penetrator. The usual design choices available to the designer are to:

[0013] a. Increase impact velocity. This is achieved by using a penetrator with a high ballistic coefficient —the ration of weight to aerodynamic drag—so it may have a high terminal velocity or by augmenting the velocity of the penetrator with a boost rocket motor.

[0014] b. Increase the weapon's cross-sectional modulus by either decreasing the cross-sectional area or increasing the weight of the penetrator. Efforts to build penetrators, for example, out of tungsten have focused on increased weight because of the increased density of tungsten compared to steel.

[0015] c. Selecting shapes having large nose factors. The nose factor term in the equation is addressed by designing tangent ogive forebodies to minimize overall nose drag.

[0016] The designer has no control over the soil factor term in the design equations.

[0017] Limited innovations have been identified in kinetic energy penetrator state-of-art over the past several decades. The art has been characterized by marginal change. The present invention provides the means to significantly increase penetration capability by departing totally from previous approaches. The invention designs a penetrator with a standoff nose pin to create a terradynamic cavity similar to the hydrodynamic cavity in supercavitating concepts in water so that the penetrator can penetrate with only the nose pin in contact with the media being penetrated. This significantly ruduces the drag of the penetrator in penetrating any media because the drag is then determined by the cross-sectional area of the nose pin and not the penetrator overall body cross-sectional area.

SUMMARY OF THE INVENTION

[0018] The present invention introduces two concepts, including:

[0019] a. A Guided Penetrator. This penetrator, because of the small diameter of its nose pin, would normally be unstable during the penetration process. It would divert from straight-line trajectory and “J-Hook”, named after the shape of the pin in ground trajectory, or reverse course to “broach” out of the ground near the initial impact point. However, the nose pin diameter, being small, offers a very low drag factor and the potential of a factor of ten increase in penetration capability compared to more conventional designs. The normally unstable penetrator can be stabilized utilizing a jet reaction control system responding to commands from an inverse angle-angle rate guidance law which determines, off-line, the control forces necessary to maintain the penetrator in a stabilized straight-line trajectory during the penetration process. A guided version of the penetrator where the inverse angle-angle rate guidance law is employed, in off-line serves to define control forces to enable the penetrator to be guided on a predetermined path using the jet reaction control system, during the penetration process while maintaining the penetrator in its cavity, offers the ability to steer the penetrator during the penetration process while maintaining a low-drag configuration.

[0020] b. A Stable Penetrator. The stable penetrator concept utilizes a nose pin diameter geometry that provides significantly reduced drag compared to conventional penetrators but is designed so that the penetrator remains stable during the penetration process. This nose pin diameter is larger than the nose pin diameter associated with a guided configuration but still provides a factor of five or more increase in penetration compared to conventional penetrator designs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 illustrates the current state of the art in penetrator concepts.

[0022]FIG. 2 illustrates a guided and unguided cavity penetrator concept utilizing a standoff nose pin.

[0023]FIG. 3 illustrates a low-drag kinetic energy cavitating penetrator using an inverse angle-angle rate guidance law providing commands to a jet reaction control system.

[0024]FIG. 4 illustrates a penetrator hydrodynamic cavity of a supercavitating penetrator.

[0025]FIG. 5 illustrates a 20 mm powder gun test facility used to verify penetrator performance in firing penetrators into a watertank to measure penetration characteristics.

[0026]FIG. 6 illustrates the cavity generated by a supercavitating penetrator penetrating into water.

[0027]FIG. 7 illustrates the results of a hydrocode or finite difference analysis.

[0028]FIG. 8 illustrates the testing of penetrators into a sandbox with velocity screens to determine penetration capability as a function of nose shape on the penetrator.

[0029]FIG. 9 illustrates the various subcaliber penetrators tested in firings into the sandbox to determine penetration as a function of the nose shape of the penetrator.

[0030]FIG. 10 illustrates penetration characteristics and drag levels associated with various penetrators fired in testing.

[0031]FIG. 11 illustrates nose pin shapes other than flat-faced nose pins that could be considered in the design of cavity penetrators to reduce the drag of guided and unguided penetrators.

[0032]FIG. 12 illustrates a stepped nose pin consisting of a small caliber nose pin stepped to a larger caliber nose pin interfacing the body diameter.

[0033]FIG. 13 illustrates the technique used to verify the existence of a terradynamic cavity.

[0034]FIG. 14 illustrates the geometry of the assembly utilized to verify the existence of a terradynamic cavity.

[0035]FIG. 15 illustrates the test facility to verify the ability of a penetrator to penetrate in a cavity mode.

[0036]FIG. 16 illustrates the tail cavity sensing geometry to verify the existence of a terradynamic cavity.

[0037]FIG. 17 illustrates the results of testing to verify a terradynamic cavity about a kinetic energy penetrator.

[0038]FIG. 18 illustrates the test set-up of a test to verify the ability of the penetrator to penetrate a water-dirt composite target.

[0039]FIG. 19 illustrates the test set-up to verify the ability of a penetrator to penetrate water and sand contained in a six foot-by six inch box.

[0040]FIG. 20 illustrates the cavity of the penetrator impacting the sandbox and not activating the delayed ignition until the penetrator has impacted the steel back-up plates.

[0041]FIG. 21 illustrates the stabilized and stable penetrator parameters for a cavity penetrator.

[0042]FIG. 22 illustrates the inverted pendulum effect on penetrators penetrating in an unstable mode.

[0043]FIG. 23 illustrates the angle-angle rate guidance concept in a constant pressure jet reaction control system approach for maintaining unstable penetrators and steering those penetrators.

[0044]FIG. 24 illustrates an inverse guidance law concept in terms of position and velocity states and co-states.

[0045]FIG. 25 illustrates the general form of a position and velocity state inverse guidance in guiding an air vehicle.

[0046]FIG. 26 illustrates the cost function associated with maintaining a kinetic energy cavity penetrator stable during penetration.

[0047]FIG. 27 illustrates the control concept of incorporating a jet reaction control stabilization system on the back of a kinetic energy penetrator.

[0048]FIG. 28 illustrates the valve plate and nozzle geometry for a jet reaction control system.

[0049]FIG. 29 illustrates the possible force states associated with an eight-nozzle control system.

[0050]FIG. 30 illustrates a control concept to eliminate overshoot in controlling a penetrator.

[0051]FIG. 31 illustrates a control logic in selecting the jet reaction control states.

[0052]FIG. 32 illustrates the approach of adding a standoff pin to existing penetrators to increase their penetration capability in a retrofit to existing inventory.

[0053]FIG. 33 illustrates a concept for retrofitting a nose pin assembly to the BLU-109 cavity penetrator.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0054] Current penetrator designs are based upon application of Young's Equation. (FIG. 1) This design evolved out of the technology base associated with the Sandia National Laboratories penetratortechnology base. Consequently, the penetrator be made out of the densest material with the bomb body having the smallest cross-sectional area possible, with a nose selected to have a high nose factor and be delivered at as high a velocity as possible compatible with the penetrator survivability and fusing constraints. The current invention departs significantly from the dictates of the conventional technology and focuses on a penetrator that is normally unstable in the penetration process. (FIG. 2) By utilizing a nose pin, or stepped nose pin, having a cross-sectional area smaller than the penetrator diameter and designed so that the nose pin creates a terradynamic cavity in which the penetrator can accomplish its penetration with the only portion of the penetrator in contact with the media being penetrated, the nose pin provides the ability to penetrate at significantly reduced drag levels compared to conventional design. This penetrator geometry, based upon the selection of the nose pin diameter and other design factors, as discussed later, can be selected so that the penetrator is either stable or unstable during the penetration process. If the nose pin diameter is selected to be small, the drag of the penetrator is significantly reduced but the penetrator would normally then be unstable. A guidance concept utilizing an angle-angle rate inverse guidance law, as taught by Mayersak (U.S. Pat. No. 5,507,452), and a jet reaction control system, as taught by Mayersak (U.S. Pat. No. 6,254,031), allows one to employ a normally unstable cavity penetrator but to maintain it in a stabilized straight-line during the penetration process. In addition, the guidance concept allows consideration of a maneuvering cavity penetrator that has the ability to follow a predetermined trajectory subsequent to impact with the target and penetration into the various media associated with the target. If the nose pin diameter is selected larger, there becomes a diameter at which the penetrator is stable during the penetration process in which guidance and control are no longer required. This nose pin geometry provides a lower drag than conventional penetrator designs and still provides enhanced penetration. The low-drag capability of a cavity penetrator is available because the drag of the penetrator, properly configured, is determined by the diameter of the nose tip and not the diameter of the kinetic energy penetrator as is the case in a more conventional design approach. The concept of using angle-angle rate space as opposed to position and velocity space and guiding the penetrator utilizing inverse guidance law techniques as taught by Mayersak (U.S. Pat. No. 5,507,452), allows the control forces to be determined beforehand in off-line trajectory analysis. FIG. 2 illustrates a typical cavity penetrator cross-section in which the nose pin diameter for a 2.75-inch diameter penetrator is stepped from one-inch down to one-half inch in a stepped nose pin geometry to provide low drag. The nose pin geometry described in this penetrator is a flat-faced nose pin.

[0055] The cavity penetrator utilizes its ability to create a terradynamic cavity about the penetrator in such a way that the penetrator touches the medium being penetrated only on its nose pin front face. The penetrator then penetrates in a very low drag geometry since the drag of the penetrator is determined by the nose pin diameter or cross-sectional area. As previously stated, this penetrator can be unstable if the nose pin diameter is selected less than certain values and may require a guidance law and control system to maintain the penetrator in a straight line or along a predetermined trajectory. The concept offers the ability to penetrate with a drag factor one-tenth of that associated with other penetrators and the ability to penetrate into targets at an overall depth of ten times that which can be reached by other penetrator geometries.

[0056] The concept of a terradynamic cavity is suggested by consideration of supercavitation penetrators designed to penetrate the water in low-drag configurations. In penetrating water, it has been long known that penetrators properly designed and propelled at a high enough velocity to generate a supercavitation envelope containing only water vapor with only the front face of the penetrator in contact with the water. The remainder of the penetrator is contained within the cavity as the penetration process continues. The cavity can be described by a parabolic equation so that the designer of a supercavitating underwater projectile can define the geometry of the projectile such that it remains in the hydrodynamic cavity during the penetration process. (FIG. 4)

[0057] Testing of kinetic energy penetrators in water to verify the ability to generate hydrodynamic cavities and to verify that the drag of the penetrator in penetrating water is determined by the forward nose geometry was accomplished in 20 mm powder gun firings into an 18-foot-long water tank. (FIG. 5)

[0058] High-speed photography of the penetrator entering the water tank at 1,320 feet-per-second clearly showed the cavity being generated by the penetrator. This cavity is in excellent agreement with the that predicted by the mathematical equations associated with a supercavitating penetrator in the penetration process. The cavity expands about the penetrator during the penetration process, reaches a maximum, and then collapses back to zero and disappears. The 35-caliber, 4.5-inch-long penetrator utilized n this test generated a cavity having a maximum diameter of approximately 3.3 inches, which also is in agreement with the state-of-the art modeling in supercavitating penetrators. (FIG. 6)

[0059] Hydrocode analysis of kinetic energy penetrators suggested that a terradynamic cavity could be formed similar to a hydrodynamic cavity in supercavitation penetration in water. This would allow the penetrator to penetrate into soil and other media with lower drag than other penetrators. The hydrocode analysis also suggested that the penetrator, unless properly designed, would be unstable during this low-drag penetration mode. (FIG. 7)

[0060] Testing was conducted where 35 caliber penetrators 4 inches in length were fired from a 20mm powder gun into a plywood box containing compressed sand and velocity screens. (FIG. 8) This testing was accomplished to determine the penetration characteristics of 35-caliber penetrators having various nose shapes. (FIG. 9) The penetrators fired into the sandbox differed one from the other by the diameter of the nose pin on the front of the penetrator. A design factor, R, which was the ratio of the diameter of the penetrator to the diameter of the nose pin, was defined to allow thresholds in penetrator stability to be determined relative to the R factor. Nose pin diameters of 0.35 to 0.10, yielding R factors from 1 to 3.5, were tested in the test series. The evidence that a cavity was formed in the penetrating test firings was suggested by predicting the penetration of the penetrator through the soil utilizing Poncelet's Equation. Poncelet's equation estimation of penetration depth and velocity is based on integration of the Poncelet equation, which in the form specific to the problem at hand is given by: ${m\frac{v}{t}} = {{0.5\quad C_{D}A\quad p\quad v^{2}} + {m\left( {g + c} \right)}}$

[0061] where v and m are the velocity and mass of the penetrator, respectively.

[0062] The first term of the right-hand side represents the drag force on the penetrator where C_(D) is the drag coefficient of the penetrator in the medium, A is the frontal area of the penetrator and p is the density of the medium. The drag coefficient depends on the shape of the penetrator and medium being penetrated and, in general, must be determined from experimental data. Typical values for a disk-shaped nose are 0.815 in water and 1.9 in sand.¹ It should be noted that the frontal area is represented by the cross-sectional area of the penetrator only in the non-cavitating case. In the hydrodynamic cavitation the frontal area is that part of the penetration which is in contact with the media being penetrated, e.g., the nose pin. In terradynamic cavitation mode, the frontal area is that part of the cross-section that is exposed to the medium, which is again, the nose pin. In order to match the velocity profile of 35-caliber penetrators penetrating into soil as determined by velocity screens, the model has to employ the cross-sectional area of the nose pin—clearly indicating that only the nose pin is in contact with the soil. The body of the dart is not contributing any drag during the penetration process. It is necessary, in order to use this phenomenon, to penetrate at velocity larger than the threshold velocity at which a cavity is created. For projectiles in water, supercavitation is typically achieved at velocities above 80 meters per second. In sand, the required minimum velocity is in the 125 to 150 meters per second range.

[0063] The second term on the right-hand side is the sum of two constants. The force mg represents the force of gravity acting on the projectile. The force mc represents a binding force exerted by solid materials on the penetrator. In the case of water, c=0. In the case of sand, c is typically on the order of 300 m/s¹. Typically, the integration is begun at some initial velocity and continued until either the velocity has reached zero, as is the case in sand, or some particular depth has been achieved. In the water the penetration velocity never reaches zero, therefore, some depth cutoff is required. Over the course of the integration, depth is continuously updated by integrating the velocity profile with respect to time.² The model has been shown to be able to predict the penetration velocities and, in turn, penetration depths in penetrators penetrating with terradynamic and hydrodynamic cavitation present with very great accuracy. The agreement between the model and the velocity profiles is excellent.

[0064] The model has been shown to be very accurate in predicting the velocity and depth of penetration. However, the model is not the goal here. The introduction of a new concept to increase penetration is. A match between the test data and Poncelet's Equation could be achieved only when the cross-sectional area in the equation was that of the nose pin diameter indicating that the drag of the penetrator was determined by the nose pin and not the body diameter of the penetrator. (FIG. 10) In addition, it was found in the testing that the ratio of penetrator diameter to nose pin diameter great than 2.5, the penetrator was unstable and tended to “J-hook” (named after the shape of the penetrator trajectory) out of the sides of the test box. One of the tests of an 0.10 diameter nose pin configured penetrator, however, penetrated in a straight line rather than diverting into an unstable of J-hook trajectory. This penetrator went completely through the entire length of the test box and exited on the far side. This penetrator utilizing conventional penetration predictions, as would all other penetrator predictions, indicates that the penetrator could not pass entirely through the five feet of sand because it did not have the correct design characteristics, in Young's Equation, to do so. This penetrator has an R factor of 3.5, indicating that very low drag projectiles could be defined if they could be maintained stable during the penetration process.

[0065] Testing and design analysis conducted in defining the current invention focused on consideration of a flat nose shape for the nose pin. (FIG. 11) It is recognized that other nose pin front-faced shapes, such as hemispherical, conical, or tangent ogive, could be incorporated into the cavity penetrator. Those nose pin shapes would reduce the penetrator cavity drag even further since these shapes are known to have less drag in penetrating soil media, concrete, and other media than a flat-nose shape. They would, however, be less stable than a penetrator using a flat nose pin shape. In addition, the testing considered a straight, single nose pin rather than a stepped nose pin geometry. A stepped nose pin geometry, for example, utilizing a hemispherical shape on the forward nose pin offers a lower drag configuration than a stepped nose geometry having a flat face on the forward nose pin. (FIG. 12) The flat-faced nose pin geometry, however, is more stable during the penetration process than a hemispherical nose pin geometry, on the forward pin of a stepped pin geometry, suggesting design trades between the nose pin length, diameter, and shape. (FIG. 12) The description of the penetrators using a 2.75-inch diameter penetrator in describing penetrator geometries is to display these concepts. The 2.75 inch diameter penetrator can be scaled directly to larger size penetrators with no loss in the ability to form a cavity or penetrator in a low drag mode. The concept scale utilizing the diameter of the penetrator as the dimensional length in a scaling process is well known in the art.

[0066] The ability to confirm the presence of a cavity in a terradynamic cavity penetrator is critical to the current invention. In order to verify that a cavity can be generated, a unique concept is defined using a delayed ignition system in the forward portion of a kinetic energy penetrator. (FIG. 13) This delayed ignition system consists of a standoff pin mounded on the body of the penetrator and a sliding sleeve and firing pin assembly which would move aft, when impacting the ground, if a cavity was not present, and, in turn, drive a firing pin to initiate a primer which would, in turn, react a marking fill. The design concept would confirm the presence of a cavity in that the terradynamic cavity, if present, would be such that the circular slider sleeve would not be in contact with the media being penetrated and the penetrating process would occur until the penetrator penetrated into a steel backstop plate which would then activate the ignition system. The cavity sensing nose pin assembly consisted of the sliding sleeve and firing pin, barrel assembly, standoff pin primer, and primer cup. (FIG. 14) The argument here is quite simple. If a terradynamic cavity is present, then the firing pin would not be driven backwards into the primer to initiate the fil in the penetrator. If a terradynamic cavity were not present, the firing pin assembly would initiate the primer system immediately on impact with the media being penetrated. A test to verify the terradynamic presence involved firing the delayed ignition penetrator from a 20 mm powder gun into a steel catch bunker with various steel targets located at various depths in compressed sand. In these tests, the projectiles penetrated through the sand with the primer system not activating until they hit the steel backstop. (FIG. 15) This testing was conducted to depths up to two feet of sand and verified in the presence of a terradynamic cavity. An estimate of the size of the terradynamic cavity was also made by incorporating an alternate ignition system primer design. In this design the tail of the kinetic energy penetrator incorporated the delayed ignition system. (FIG. 16) The delayed ignition system here would move the tail fin and primer backwards to impact a firing pin in the event that the tail touched the media being penetrated, the tail being forced rearward into a firing pin setting off a primer and, in turn, setting off the marking of the penetrator. The argument here is that if the tail did not activate the primer until the penetrator cavity sensing assembly hit a steel target, then a cavity was present and the dimensions of the cavity at the rear of the penetrator were at least as large as the span of the tail fins. Testing of both forward delayed ignition and rear delayed ignition systems demonstrated that a terradynamic cavity was present. (FIG. 17) They also demonstrated that this cavity was sufficiently large to allow the tail fins to clear the cavity. Consequently, a delayed ignition system, which requires a cavity to function, can be used in a hydrodynamic cavity or terradynamic cavity as a means for penetrating sand, water, and water and sand interfaces by managing the penetrator drag during the penetration process through the selection of the nose pin diameter.

[0067] A test of the cavity penetrator in a composite water-sand interface was accomplished utilizing the 20 mm powder gun water tank test facility. (FIG. 18) The test set-up here positioned a box of compressed sand with a water distance of ten feet backed by two steel back-up plates. The 20 mm powder gun fired the cavity penetrator into the water with the forward nose delayed ignition system through the water tank into the sand and into the metal plate back-stop. (FIG. 19) In the penetration process, the penetrator impacted the water at 1,320 feet per second and created a cavity that is expected in the supercavitation penetration of water. It then penetrated into the wooden sandbox and through the sand and out the backside impacting a steel plate, at which point the primer reacted. The 56-microsecond delay on the primer allowed the penetrator to pass through both steel plates before the primer was fired. The penetrator then re-established the supercavitation cavity and continued to penetrate. This test verified the ability of a cavity penetrator to transition from a hydrodynamic cavity to a terradynamic cavity and back to a hydrodynamic cavity while maintaining its low-drag characteristics.

[0068] The options open to the penetrator designer focused on a cavity penetrator are significantly more complicated than those associated with conventional penetrator designs as dictated in Young's Equation. The penetrator length, diameter, nose pin length, nose pin diameter, nose pin shape, penetrator static margin, R factor and length are all factors. (FIG. 21) However, the static margin of the penetrator and the location of the center of gravity of the penetrator become very important since these are factors affecting whether or not the penetrator is stable in its penetrating cavity during the penetration process. There are essentially two approaches which the invention addresses, including:

[0069] a. A Stabilized or Guided Low-Drag Penetrator. This penetrator employs a penetrator geometry that normally would be unstable in the penetration process. The diameter of the body-to-nose tip diameter ratio is of the order of 2.5 and the penetrator is maintained stable or guided along predetermined paths using, typically, an angle-angle rate inverse guidance law and a jet reaction control system as taught by Mayersak. In the stabilized penetrator design the nose pin diameter is selected to provide an R factor less than 2.5. The other factors, such as the shape of the nose pin, whether or not a stepped nose pin is used, the static margin of the penetrator, and the like are selected such that the penetrator would be stable during the cavity penetrator penetration process. This approach would define a penetrator having much lower drag in the penetration process than defined by conventional design approaches. The stable cavity penetrator approach is one that can enhance existing inventory penetrators such as the BLU-109 by modifying the penetrator to incorporate a standoff nose pin such that the body of the penetrator-to-nose tip diameter ratio is 2.5 or less providing lower drag penetration than the conventional BLU-109 geometry. This cavity penetrator nose tip kit could then be retrofit to existing inventory BLU-109 systems to reduce the drag of these penetrators in penetrating into targets and enhancing their overall utility in engaging hardened targeted, buried targets, and deeply hardened buried targets.

[0070] The design of the cavity penetrator where the penetrator would normally be unstable requires that a concept be identified to maintain the penetrator in a straight line to penetration or to maintain the penetrator in a predetermined trajectory during the penetration process. An inverse guidance law using an angle-angle rate states an inverse guidance concept coupled with a jet reaction stabilized control system overcomes the effect of the instability. The concept is similar to attempting to balance a clock pendulum on one's finger-tip with the pendulum weight overhead. (FIG. 22) The line of action of the supporting force to the tip of the pendulum will not pass through the center of gravity of the pendulum and the penetrator will fall off either left or right. The same is true of a kinetic energy cavity penetrator penetrating in a cavity mode since all of the forces being experienced by the penetrator are passing through the nose tip of the generator and any time that the nose tip forces pass outside the center of gravity the penetrator then starts to enter into an unstable trajectory mode. The inverse pendulum problem can be resolved by placing a stabilization system in the penetrator, which would normally be unstable in penetration and maintaining that penetration stable.

[0071] A concept using an inverse guidance law operating with an angle-angle rate state offers the ability to maintain the penetrator by defining co-states which will yield, during the trajectory, in a straight-line penetration or to maintain the penetrator along a predetermined trajectory utilizing a Constance pressure jet reaction control system. Since the penetration process associated with high penetrator velocity at impact with the media to be penetrated occurs very rapidly, the control forces needed to have a guidance concept that enables the control force required to maintain stable penetration to be determined essentially instantaneously. (FIG. 23) Mayersak teaches an inverse guidance concept which enables guidance without an inertial element in a position and velocity state by formulating the guidance law as a calculus of variations problem and defining co-state vectors which are time varying vectors which would allow the trajectory requirements in terms of six-degrees-of-freedom trajectory to be met while at the same time satisfying the parametric constraints based upon the trajectory in terms of the calculus of variations problem. In his U.S. Pat. No. 5,507,452, Mayersak teaches a concept where the position and velocity is fed in as inputs into a polynomial network or neural network concept with the target location defined to allow command equations to be generated in terms of position and velocity states and as a function of the co-state parameters. (FIG. 24) A guidance law form has been evolved in which the guidance law requires minimum angle of attack or control force while at the same time maximizing terminal velocity and satisfying equations of motion through the use of the LaGrange time or co-state vectors. This particular guidance law, formulated by Mayersak, requires vertical descent and zero miss distance as initial conditions on the inverse trajectory integration. The approach in solving the guidance law is to integrate the trajectory equations backward into the control space and select those trajectories that meet the launch conditions from which the various trajectories run. Having done this, one automatically has the ability to determine control forces necessary as a function of position and velocity in the control space to achieve the trajectory desired. (FIG. 25)

[0072] An alternate form of the inverse guidance law and angle-angle space is one in which the terminal velocity vector is minimized in the vertical and in which the angle rate is minimized in the cost function. This problem can be formulated as a variation of the inverse guidance law taught by Mayersak, or in terms of slide slip and angle of attack. This can be envisioned in terms of one plane. Here position and velocity states become the angle and angle rate state space in determining an off-line backwards integration, to define the control equations in terms of the co-states. This provides a means for determining the forces necessary, given the angle and angle rates at a particular point, to maintain the penetrator in a straight-line penetration or along a predetermined trajectory. (FIG. 26) Knowing the control force required through the inverse guidance law then requires a control system capable of providing that control force. A jet reaction control system, also described by Mayersak, has the ability to provide the stability control for the penetrator during the penetration process. (FIG. 27) The jet reaction control system taught by Mayersak utilizes a valve plate assembly consisting of four bi-directional nozzles with a dual-action solenoid positioned over each nozzle assembly such that it controls poppet valves so that the flow from the hot gas generator can be open at all times so that the gas generator can be maintained at constant pressure. The four-nozzle configuration can generate maximum thrust or alternate thrust configurations by firing the nozzles in appropriate pairs. When nozzles are fired left and right out of the same assembly a neutral state for that nozzle is obtained and the other two nozzles can then provide thrust with the jet reaction control system responding to commands from the inverse angle-angle rate guidance law. (FIG. 29)

[0073] The use of a jet reaction control system also allows a unique control concept to be incorporated wherein an accelerometer would measure, in a one plane control concept for example, when the angle of attack passed a selected dead band which triggers the driver. (FIG. 30) This drive approach is one of several which could be employed to maintain the cavity penetrator stable during its penetration or maneuvering the penetrator along a predetermined path during the penetration. Since the penetration process is inherently very rapid, the use of a computer to calculate the control forces necessary is prohibitive since time required to effect these calculations is more than the time available to calculate the control force. (FIG. 31) An approach using a state machine controller with shift registers offers the ability to control the cavity penetrator during the penetration process. An acceleration module would determine acceleration states and provide these to the state machine using comparative techniques on a 15 nanosecond-sampling to determine when control forces are required. This state machine would utilize inverse trajectory control forces generated off-line and stored in the machine to determine the corrective force necessary which would be provided, in turn, to a JRC system logic utilizing a digital clock to time-out T₁ and T₂ times allowing the appropriate jet reaction control system states to be selected during the penetration process to maintain the penetrator on a stable penetration or along a predetermined trajectory when penetrating in what normally would be an unstable cavity penetrator mode.

[0074] The concept of retrofitting existing inventory penetrators such as the BLU-109, the J-1000, and the all up penetrator to incorporate a standoff nose pin in the forward fuse well, for example, in such a way as to increase the penetration capability of these penetrators by creating a cavity penetrator geometry, which is stable because the selection of the nose pin geometry, meets the criteria for stable penetration and offers the ability to significantly increase the performance of these penetrators. (FIG. 32) A retrofit kit which would retrofit on the front of existing inventory weapons to generate a cavity to enhance penetration but sized such that the penetrator will penetrate into cavity penetration mode in a stable trajectory offers to increase the penetration capability of existing penetrators by a factor of two or more. 

I claim:
 1. In a terradynamic penetrator having an elongated body, the improvement comprising: a nose pin attached to the elongated body at a first end, said nose pin sized relative to a size of the elongated body to create a terradynamic cavity in a target through which said body passes substantially entirely within said cavity.
 2. The terradynamic penetrator in accordance with claim 1, in which said nose pin is of stepped configuration.
 3. The terradynamic penetrator in accordance with claim 1, in which a diameter of said nose pin relative to a diameter of said body is in a range of 1 to 3.5 or less. 4-11. (Canceled)
 12. The terradynamic penetrator in accordance with claim 1, in which said nose pin is flat-faced.
 13. The terradynamic penetrator in accordance with claim 1, in which said nose pin includes a forwardly-facing surface of any of round, conical, ogival and spherical configuration.
 14. The terradynamic penetrator in accordance with claim 1, in which said nose pin is of tapered configuration.
 15. (Canceled)
 16. The terradynamic penetrator in accordance with claim 1, including a delayed ignition system.
 17. The terradynamic penetrator in accordance with claim 3, wherein the diameter of said nose pin relative to the diameter of said body is less than 1 to 2.5.
 18. The terradynamic penetrator in accordance with claim 17, wherein the diameter of said nose pin relative to the diameter of said body is about 2.5.
 19. A penetrator comprising: an elongated body; and a nose cap on a first end of the elongated body, wherein the elongated body has an outer surface having a first diameter, wherein the nose cap has an outer surface having a second diameter, and wherein a ratio of the first diameter to the second diameter is in a range of 3.5:1 to 1:1.
 20. The penetrator of claim 19, wherein the ratio is about 2.5:1.
 21. The penetrator of claim 19, wherein said nose cap is of stepped configuration having a first stepped diameter at a distal end from the elongated body and a second stepped diameter at a proximal end toward the elongated body, the first stepped diameter less than the second stepped diameter.
 22. The penetrator of claim 19, wherein the ratio is from 2.5:1 to 1:1.
 23. The penetrator of claim 22, wherein the ratio is about 1:2.5.
 24. The penetrator of claim 19, wherein the nose cap includes a forwardly-facing surface at a distal end from the elongated body, the forwardly-facing surface have a shape selected from the group consisting of round, conical, ogival and spherical.
 25. The penetrator of claim 19, wherein the nose cap is of tapered from a base at a proximal end toward the elongated body to a distal end from the elongated body.
 26. The penetrator of claim 19, comprising a stabilizer.
 27. The penetrator of claim 26, wherein the stabilizer employs an angle-angle rate inverse guidance law.
 28. The penetrator of claim 26, wherein the stabilizer includes a jet reaction control system. 